Li-6 MAS NMR has been used to study the lithium local environments and manganese electronic structures of a number of lithium manganese oxides with manganese oxidation states varying from (III) to (IV). Most samples were chosen with compositions within the LiMn2O4-Li2Mn4O9-Li4Mn5O12 phase diagram, but Li2Mn2O4 with Mn(III) was also synthesized for comparison. Despite the presence of unpaired electrons, high-resolution spectra could still be acquired, allowing a number of different local environments to be detected. Assignments of the resonances to different lithium local environments were made by comparing the observed shifts and local structures in a number of lithium manganates. Two Li-6 NMR resonances were observed for the spinel phase Li4Mn5O12 at 1980 and 847 ppm, which were assigned to Li+ in the octahedral and tetrahedral sites of the spinel structure, respectively. A shift was observed for Li+ in the tetrahedral site of Li2Mn4O9, which also contains Mn(IV), at 687 ppm. The shifts:are ascribed primarily to a Fermi-contact shift mechanism, and possible mechanisms to account for the directions and sizes of the shift are discussed. Shifts to lower frequency are observed as the manganese oxidation state is reduced (i.e., for manganates containing occupied e(g) orbitals). The Li-6 MAS NMR spectra of the spinels with a Li:Mn ratio of 1:2 are extremely sensitive to the synthesis conditions. When relatively high synthesis temperatures (850 degrees C) are used, a single resonance at 520 ppm, from the normal spinel phase, dominates. In contrast several resonances are observed for samples synthesized at lower temperatures (550-650 degrees C), as a result of defects in the normal spinel structure. These resonances collapse into the main spinel resonance at high temperatures (250 degrees C) and are assigned to electronic defects associated with higher oxidation state manganese ions (Mn4+)No evidence for a Jahn-Teller distortion is observed in both the NMR and by diffraction for samples that contain considerable-disorder. In contrast, samples that were prepared at temperatures of 650 degrees C or higher show a cubic-to-tetragonal phase change below room temperature. This is accompanied by the appearance of at least three additional Li-6 resonances, indicating some ordering of the Mn3+ and Mn4+ cations below the phase transition, in the time scale of the NMR experiment.